Understanding the following step in MATLAB

Hello all, I came across the following code on MATLAB but not getting its last step:

symbols = randi([0 3], 1, 256);

constellation = [1+1i, -1+1i, -1-1i, 1-1i];

signal = constellation(symbols + 1); % Last step

My query is why " symbols +1 " is written in last step and why not only " symbols".

Any help in this regard will be highly appreciated.

Answer 1

[the cyclist]

The line

symbols = randi([0 3], 1, 256)

generates random values from the values [0 1 2 3]. Those zero values are not a valid index int the constellation vector, in other words

constellation(0)

would throw an error, because there is no "zeroth element". So, I presume this person adds the 1 to get valid indexing.

They could also have done

symbols = randi([1 4], 1, 256); % Note that I changed the random numbers generated
constellation = [1+1i, -1+1i, -1-1i, 1-1i];
signal = constellation(symbols); % Note that I took away the +1

I'm not sure why they did not code it this way, but maybe the zeros are need later.

[charu shree]

@the cyclist, Thanks a lot sir for such a wonderful response...

Answer 2

[Paul]

The elements in symbols range from 0 - 3, but Matlab uses 1-based indexing, i.e. the indices int0 constellation can only be 1-4.

[charu shree]

@Paul, Thank u so much sir for the reply...